Merge pull request knaxus#62 from knaxus/problems

New Problem: kth max & min in BST

Author: TheSTL

README.md

@@ -37,7 +37,9 @@ Collection of interview questions with Unit Tests. Problems includes Data Struct
 - [Doubly Linked List](src/_DataStructures_/DoublyLinkedList)
 
 - [Trees](src/_DataStructures_/Trees)
-  - [Binary Search Tree](src/_DataStructures_/Trees/BST)
+  - [Binary Search Tree](src/_DataStructures_/Trees/BinarySearchTree)
+    - [Find k<sup>th</sup> maximum in a BinarySearchTree](src/_DataStructures_/Trees/BinarySearchTree/find-kth-max)
+    - [Find k<sup>th</sup> minimum in a BinarySearchTree](src/_DataStructures_/Trees/BinarySearchTree/find-kth-min)
   - [Suffix Tree](src/_DataStructures_/SuffixTree)
 
 ### Logical Problems

src/_DataStructures_/Trees/BST/Node.js src/_DataStructures_/Trees/BinarySearchTree/Node.js

@@ -0,0 +1,38 @@
+const BST = require('../index');
+
+// Inorder traversal returns a sorted array
+function inOrderTraversal(root) {
+  if (root === null) return [];
+  let arr = [];
+  // traverse left
+  const left = inOrderTraversal(root.leftChild);
+  arr = [...left, root.value];
+  const right = inOrderTraversal(root.rightChild);
+  return [...arr, ...right];
+}
+
+function findKthMax(rootNode, k) {
+  const arr = inOrderTraversal(rootNode);
+  if (k <= 0 || k > arr.lenth) {
+    throw new Error('Invalid value for K');
+  }
+  return arr[arr.length - k];
+}
+
+// // create a BST
+// const myBST = new BST(6);
+
+// myBST.add(2);
+// myBST.add(19);
+// myBST.add(14);
+// myBST.add(8);
+// myBST.add(5);
+// myBST.add(12);
+// myBST.add(33);
+// myBST.add(52);
+// myBST.add(1);
+
+// // find 3rd max
+// console.log(findKthMax(myBST.root, 3));
+
+module.exports = findKthMax;

src/_DataStructures_/Trees/BinarySearchTree/find-kth-max/index.js

@@ -0,0 +1,40 @@
+// eslint-disable-next-line no-unused-vars
+const BST = require('../index');
+
+// Inorder traversal returns a sorted array
+function inOrderTraversal(root) {
+  if (root === null) return [];
+  let arr = [];
+  // traverse left
+  const left = inOrderTraversal(root.leftChild);
+  arr = [...left, root.value];
+  const right = inOrderTraversal(root.rightChild);
+  return [...arr, ...right];
+}
+
+function findKthMin(rootNode, k) {
+  const arr = inOrderTraversal(rootNode);
+  if (k <= 0 || k > arr.lenth) {
+    throw new Error('Invalid value for K');
+  }
+  return arr[k - 1];
+}
+
+// // create a BST
+// const myBST = new BST(6);
+
+// myBST.add(2);
+// myBST.add(19);
+// myBST.add(14);
+// myBST.add(8);
+// myBST.add(5);
+// myBST.add(12);
+// myBST.add(33);
+// myBST.add(52);
+// myBST.add(1);
+// myBST.add(0);
+
+// // find 3rd max
+// console.log(findKthMin(myBST.root, 3));
+
+module.exports = findKthMin;